Filters are useful in a variety of contexts. For example, filters are often used in electrical or optical equipment. An air pressure differential between the interior and exterior of a housing containing the equipment can be produced as the electrical or optical equipment heats and cools. Often the housing includes a vent to allow air flow that equalizes the pressure. A filter is typically provided over the vent to reduce the flow of contaminants into and/or out of the housing.
Computer disk drives, and in particular, hard disk drives, are one example of a device that uses filters in this manner. Disk drives are sensitive to moisture, chemical contamination, and particulate contamination, particularly, as the drive heads become smaller and aerial densities increase. Chemical contaminants, such as hydrocarbons acid gases, can condense onto a disk and degrade the head/disk interface and/or corrode the heads. Particulate contaminants can lead to stiction and can cause read/write errors and head crashes.
A filter placed over a vent in a disk drive typically includes filter material that filters particles and contaminants from the air. To increase the lifetime of filter material, particularly adsorbent filter material, a long and narrow flow path is often provided within the walls of the housing or in a cover disposed against the housing so that air flows along the path, through the filter, and into the interior of the housing. This path is often referred to as a "diffusion channel". The presence of a diffusion channel can reduce the amount of chemical contaminants and moisture reaching the adsorbent material of the filter and/or the inside of the disk drive.
Conventionally, a diffusion channel in a base or cover of a housing is made by casting or stamping the channel in the base or cover. Both of these methods provide challenges for tool makers and are difficult to change. Another technique includes providing the diffusion channel in a plastic body that is then attached-to the housing. This requires additional plastic and takes up vital space in the drive. Thus, there is a need for new diffusion channel designs.